| Abstract
| - The layered silicic acid H-magadiite and the corresponding Na+ salt have been investigatedby a combination of three spectroscopies: 29Si nuclear magnetic resonance, infraredabsorption, and Raman scattering. When sodium ions are exchanged with protons, theresulting H-magadiite does not swell any more and displays a less crystalline structure thanthe corresponding Na sample. Similar low crystallinity is also observed in fully dehydratedNa-magadiite samples, which clearly reveals that water molecules play a crucial structuralrole for local ordering, which must be taken into account. Indeed, by combining threespectroscopic techniques under various hydration conditions, several vibrations bands ofthe silicate layers can be assigned precisely, leading to refined structural information. Inparticular, assignments in the spectral region corresponding to the vibrations of silicatelayers reveal three hydration states that can be correlated to previous observations on thestretching and bending OH vibrations, which evidenced three distinct organizations ofadsorbed water molecules.
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